This invention relates to polypropylene which has a high organic peroxide content.
It is known in the art that the molecular weight of polypropylene can be controlled by the addition of organic peroxides which will degrade the molecular weight of the polymer. Usually an organic peroxide is added to the polypropylene which is then heated to the organic peroxide's decomposition temperature where the organic peroxide proceeds to break the long polypropylene polymer chains apart.
It is also known in the art that masterbatching can be used to facilitate this process. The term "Masterbatching" as used in this disclosure is the process of adding a small amount of polypropylene, which has an organic peroxide and/or other additives within it, to a larger amount of polypropylene and subsequently blending and extruding in order to achieve the desired polypropylene characteristics. The term polypropylene as used in this disclosure and in the art refers to a homopolymer of propylene or a copolymer of propylene and another alpha-olefin. Furthermore, blending and extruding as referred to above are general references to procedures in the art used for processing polypropylene.
One problem in the art is the melt blending of large amounts of peroxide into polypropylene. This is difficult because the peroxide tends to decompose during the melt blending step. While some of the peroxide can survive the melt blending step, at least some of the peroxide degrades the polypropylene. Another problem with mixing solid polypropylene pellets, flakes, or powder, with a liquid organic peroxide, is that, the polypropylene does not usually form a homogeneous, free-flowing, phase with the liquid organic peroxide. Usually, an absorbant, such as silica, is added to the polypropylene in order to facilitate the addition of organic peroxide in the masterbatching process. However, absorbant which is added to the polypropylene can interfere with the processing of the polypropylene material. Therefore, polypropylene which could absorb liquid organic peroxide without the necessity of using other absorbants, such as silica, would be of great economic and scientific value.